Gabe Mirkin, M.D.
The Glycemic Index measures how high blood sugar
levels rise 30 to 120 minutes after eating a particular food or
combination of foods. A study from Loughborough University in
England shows that athletes in sports events lasting more than a
couple hours may benefit from a pre-competition meal that has a
low glycemic index (American Journal of Clinical Nutrition,
August 2006).
How long you can exercise a muscle without hurting
depends on how much sugar you can store in that muscle and
how long you can keep that sugar in the muscle during
competition. Just about everyone agrees that taking extra
carbohydrates for two or there days prior to an endurance
competition can help fill your muscles maximally with stored
sugar and therefore increase endurance. A well-trained athlete
can also fill his muscles maximally with sugar just by cutting back
on workouts for a few days prior to competition, no matter what
he eats.
Since it takes up to 24 hours to fill your muscles
maximally with sugar, the pre-race meal is not used for that
purpose. This new study showed that a low-glycemic index meal
taken three hours prior to competition may help an athlete to
exercise longer by causing muscles to use more fat, and less
sugar, for energy. While nobody really knows why, the most
likely explanation is that when blood sugar levels rise too high,
the pancreas releases huge amounts of insulin. Insulin drives
sugar into cells and causes cells to burn more sugar. This uses
up sugar more quickly. On the other hand, the low-glycemic meal
does not cause a high rise in insulin, so muscle burn more fat,
preserve their stored sugar supply and can be exercised longer.
More on the Glycemic Index
September 15, 2006